The overall capacities of broadband satellites are increasing exponentially, and such capacity increases present unique challenges in the associated ground system and network designs. The goal of the system designers, system operators, and service providers is to support and provide efficient, robust, reliable and flexible services, in a shared bandwidth network environment, utilizing such high capacity satellite systems. In prior satellite communications systems, the downlink data channels (i.e., transmission of data from the satellite to the satellite terminal) typically utilized bandwidths on the order of 20 MHz or less. In such systems, due to the narrow bandwidth being utilized, there was typically no need to provide for equalization in the demodulator/modem portion of the receiver, as the amplitude and phase distortions of the components where substantially constant.
However, in current systems, such as Digital Video Broadcasting, Second Generation (DVB-S2) satellite communications systems, for example, as the need for additional bandwidth in the downlink data channels of satellite communications systems becomes necessary in order for such systems to provide various applications (e.g., high internet access capability) to end users, there is also a need to provide equalization in the demodulator/modem portion of receiver channel of the system, such as for signal phase and amplitude distortions, which can become significant over a wideband channel. Such amplitude and phase distortions must be negated or compensated for in order for proper receipt and demodulation of the incoming data signal. Additionally, addressing phase and amplitude distortions must also be done at a reasonable cost.
Demodulators for satellite communications systems (e.g., DVB-S2 type demodulators) typically perform equalization of data samples and error samples of the incoming data signals after the carrier recovery. Such equalization is typically performed by a Finite Impulse Response (FIR) filter and the error computation is performed locally after the Carrier Synchronization Module (CSM) block. However, where the demodulator performs the equalization before frame-timing recovery and carrier recovery, as, for example, at a Jupiter terminal of the Jupiter satellite system, a significantly better performance in Unique Word (UW) detection in the Unique Word processor (UWP), and in phase and frequency estimation in the CSM, is possible. Therefore, better carrier recovery typically can result.
Examples of demodulation in satellite communications systems are described in U.S. Pat. No. 6,985,523 to Sims et al., titled “Method and System for Adaptive Equalization for Receivers in a Wide-Band Satellite Communications System,” and in U.S. Patent Application Publication No. 2002/0131528 to Clewer et al., titled “System and Method of Parallel Partitioning a Satellite Communications Modem,” the entireties of which are incorporated herein by reference. Further an example of automatic gain control and demodulation in satellite communications systems is described in U.S. Pat. No. 6,904,273 to Steber et al., titled “Method and System for Automatic Gain Control in a Satellite Communications System,” the entirety of which is incorporated herein by reference.
But, even where the demodulator performs the equalization before frame-timing recovery and carrier recovery, the error computation still takes place after the carrier recovery, which typically results in the introduction of an arbitrary delay between the input samples and the error samples. Thus, a need exists to synchronize the data samples and error samples in relation to equalization of the incoming data signals as to such arbitrary delay, particularly for continuous mode data transmission, as well as for intermittent, or bursty, data transmission in the burst mode of data transmission. And, therefore, a need exists for demodulation methods and apparatus, such as, for example, with Least Mean Squares (LMS) adaptive filtering, that addresses the input data samples and error samples being properly synchronized, in view of an arbitrary delay introduced in processing data signals, such as where a demodulator performs the equalization before frame-timing recovery and carrier recovery, particularly in a continuous mode of data transmission.
Current systems can therefore fail to support, in this regard, efficient, robust, reliable and flexible broadband services, in such shared bandwidth network environments, utilizing such high capacity satellite systems. Achieving efficient, robust, flexible and fast broadband services, in such a high capacity, shared bandwidth, satellite system network, therefore can pose unique challenges to system designers and operators.
Accordingly, there exists a need for cost effective methods and apparatus for equalizing the incoming wideband data signals to compensate for amplitude and phase variations in the demodulator/modem portion of the receiver over a given bandwidth when signals are input for reception and processing, particularly in a continuous mode of data transmission, which promotes increasing accuracy in processing the received signals, effectively maintaining a lock on the data signals after acquisition of the signals for processing the input data, and minimizing degrading the accuracy of phase and frequency estimation for the signal or data processing.
Accordingly, there exists a need for a cost effective method and apparatus for accurate synchronization in processing of data frames transmitted, particularly in a continuous mode of data transmission, from a high capacity, shared bandwidth communications network, such as a satellite communications network, or a computer communications network, that employs a dynamic and flexible architecture, apparatus and methods to synchronize the error samples and the input data samples, which would meet various requirements and desires associated with efficient, robust, reliable and flexible broadband services in a high capacity, shared bandwidth, satellite network, and that would be relatively efficient and automated from a network management and load balancing standpoint.